1. Field of the Invention
The present invention relates to a light-emitting diode (LED) package structure. More particularly, the present invention relates to a light-emitting diode package, which can enhance the efficiency thereof.
2. Description of the Related Art
Light-emitting diode fabricated using a semiconductor compound formed from group III-N semiconductors is a light emitter with a wide bandgap. In general, the light-emitting diode is able to emit light with a wide specrum, that is, from the infrared to the ultraviolet. The basic structure of an LED device includes a P-type and an N-type epitaxial layer fabricated using a compound of the III-V semiconductors and a light-emitting layer sandwiched between the two epitaxial layers. In general, the light-emitting efficiency of the LED device depends on the internal quantum efficiency of the light-emitting layer and the light extraction efficiency of the device. The internal quantum efficiency can be increased through any improvement in crystal quality and the structural design of the light-emitting layer. The light extraction efficiency, on the other hand, can be increased through a reduction in the energy loss due to total internal reflection of light emitted by the light-emitting layer within the LED chip.
At present, the anode and the cathode of a gallium nitride (GaN) LED device grown on sapphire are set up on the same side with both the anode and the cathode capable of reflecting light. Hence, most high efficiency GaN/sapphire LED deploys a flip-chip package design so that the anode and the cathode face the non-transparent package substrate called submount. Furthermore, a reflective layer is also formed on the epitaxial layer facing the package substrate so that most of the light is emitted from the opposite side of the anode and the cathode. Another advantage of using a flip-chip design is that, together with a suitable sub-mount such as a silicon substrate, the thermal characteristics of the device can be enhanced when the device operates with a large current. As a result, not only is the light extraction efficiency of the LED increased, the internal quantum efficiency of the LED is also sustained due to rapid heat dissipation.
In the aforementioned light-emitting diode with a flip-chip package design, the degree of shielding by the non-transparent anode and cathode is greatly reduced so that overall light-emitting efficiency is increased. In addition, the rate of heat dissipation from the device is also increased so that the device can have a longer lifetime. However, light emitted from the lateral surfaces of the light-emitting diode is never utilized effectively.